Inkjet printing mechanisms use pens which shoot drops of liquid colorant, referred to generally herein as "ink," onto a page. Each pen has a printhead formed with very small nozzles through which the ink drops are fired. To print an image, the printhead moves back and forth across the page shooting drops as it moves. Typically, a service station is mounted within the printer chassis to clean and protect the printhead. For storage, or during non-printing periods, the service stations usually include a capping system which humidically seals the printhead nozzles from contaminants and drying. Some caps are also designed to facilitate priming, such as by being connected to a pumping unit that draws a vacuum on the printhead.
During operation, clogs in the printhead are periodically cleared by firing a number of drops of ink through each of the nozzles in a process known as "spitting." In the past, the waste ink was collected in a reservoir portion of the service station, which is often referred to as a "spittoon." After spitting, uncapping, or occasionally during printing, most service stations have an elastomeric wiper that wipes the printhead surface to remove ink residue, as well as any paper dust or other debris that have collected on the printhead.
To improve the clarity and contrast of the printed image, recent research has focused on improving the ink itself. To provide faster, more waterfast printing with darker blacks and more vivid colors, pigment based inks have been developed. These pigment based inks have a higher solid content than the earlier dye based inks. Both types of ink dry quickly, which allows inkjet printing mechanisms to use plain paper. Unfortunately, the combination of small nozzles and quick drying ink leaves the printheads susceptible to clogging, not only from dried ink and minute dust particles or paper fibers, but also from the solids within the new inks themselves.
Partially or completely blocked nozzles can lead to either missing or misdirected drops on the print media, either of which degrades the print quality. Thus, spitting to clear the nozzles becomes even more important when using pigment based inks, because the higher solids content contributes to the clogging problem more than the earlier dye based inks. Unfortunately, while spittoons were suitable for the earlier dye based inks, they suffer a variety of drawbacks when used with newly developed pigment based inks.
For example, during spitting the inkjet pens are positioned over the spittoon, which consumes valuable printing time, not only to spit, but to position the printheads over the spittoon, and then return the printheads to the page for printing. This time consumption decreases the throughput of the printing mechanism, which is a rated characteristic, often measured in pages per minute. Consumers desire faster printing mechanisms, and those with a lower throughput rating are considered less desirable. As a design compromise, to minimize the loss of page throughput, less time could be devoted to spitting. Unfortunately, this compromise often results in poor quality printed images, from the omission of dots being printed due to clogged nozzles. Thus, in the past there has been an unsatisfactory trade-off between throughput and print quality.
Thus, a need exists for an improved inkjet printhead servicing system, which is directed toward overcoming, and not susceptible to, the above limitations and disadvantages.